House Speaker Paul D. Ryan (R-Wis.) gives a presentation on Capitol Hill. (Michael Reynolds/European Pressphoto Agency)

Benjamin Sommers is an associate professor of health policy and economics at the Harvard T.H. Chan School of Public Health and a primary care physician at Brigham & Women’s Hospital in Boston. From 2011 to 2016, he served as an adviser in the U.S. Department of Health and Human Services.

Republican leaders in Congress have at last unveiled their proposal to overhaul the Affordable Care Act. In a nod to a growing number of Republicans concerned that a full repeal would undo coverage gains in their home states, the new plan at first glance appears to protect coverage for those insured under the ACA’s Medicaid expansion.

This is a shift from prior Republican health-care legislation — including a plan from new Health and Human Services Secretary Tom Price and the 2015 ACA repeal bill passed by Congress (and vetoed by President Obama), both of which explicitly eliminated the Medicaid expansion. But the fine print of the new proposal instead takes a more insidious approach to gutting the Medicaid expansion.

The bill states that anyone experiencing more than a one-month gap in coverage after 2019 would no longer be eligible for the generous 90 percent federal funding the ACA provided to help states expand Medicaid to the working poor. While this may seem like a reasonable way to protect coverage for those who already have it, in practice this means that the Medicaid expansion would wither on the vine and could shrink to nearly nothing in just a few short years.

Why? Research over the past decade has documented that coverage in Medicaid is unstable over time. People frequently move in and out of coverage, a phenomenon often called “churning.” In part, this relates to the program’s administrative features that require frequent eligibility reverification and renewal applications for beneficiaries to maintain coverage — more on that shortly. But it also relates to the fundamental nature of a health-care safety-net program. Eligibility for Medicaid fluctuates with job losses or new employment, seasonal work or overtime, changes in family circumstances such as marriage or divorce and other factors.

One study of Medicaid data found that the average enrollee receives Medicaid coverage for only 78 percent of the year, and this figure drops to 68 percent when focusing just on non-elderly, non-disabled adults, the main beneficiaries of the ACA expansion. Another study of national survey data found that 43 percent of adults in Medicaid had experienced a gap in coverage within the first 12 months of enrolling, and 55 percent had a gap within 23 months.

In other words, under the GOP bill, the majority of the Medicaid expansion population under the ACA would likely become ineligible for the current level of federal funding in less than two years.

But that’s not all. In addition to changes in eligibility, another frequent cause of churning is the Medicaid renewal process. Coverage in Medicaid is time-limited, and beneficiaries must periodically demonstrate their eligibility to stay in the program. The ACA made significant strides in reducing the hassle of applying for and retaining Medicaid coverage, which has produced large enrollment gains even among those already eligible for the program before 2014.

But the new GOP bill takes steps in the opposite direction. The bill creates a new requirement that states conduct eligibility re-determinations every six months, rather than annually as under the ACA. It also reduces the ability of states to use “presumptive eligibility,” which allows hospitals and other entities to temporarily enroll applicants in Medicaid before their eligibility can be verified. Finally, the bill limits retroactive Medicaid coverage to no more than a month, compared with the current practice of 90 days. This grace period is often critical for people who enroll in Medicaid during health emergencies.

Every eligibility re-determination or other enrollment obstacle in Medicaid is an added opportunity for people to fall through the cracks. As a primary care physician, I have seen this countless times. Patients show up for their appointments, only to learn that their Medicaid coverage has lapsed. Our office promptly helps them sign up again, which usually minimizes the disruption to their medical care. But under the GOP bill, people who have moved, lost their mail, filled out a form incorrectly or forgot they needed to renew by a certain date would not lose coverage temporarily — it would likely be lost forever.

Putting the pieces together, the GOP bill says that people who have Medicaid expansion coverage can keep it — and by extension, expansion states, hospitals and providers can keep their funding. But in practice, the bill would use churning in Medicaid as a vehicle for dramatically cutting federal support for expansion within just a few years. Worse than that, the bill would make enrollment and renewal of Medicaid coverage even harder, thereby accelerating the expansion’s demise.

As consumer groups, providers and expansion-state policymakers consider the GOP’s new “repeal and replace” bill, they should not be deceived by appearances. The ACA’s Medicaid expansion remains squarely in the crosshairs, even if this time the hunters are camouflaged.